As ultra high integration in semiconductor devices increasing in recent years, manufacturing superfine metal wirings that conform to rigorous design rules has become a crucial technical requirement. However, when the aluminum wirings normally utilized in the prior art, such as wirings constituted of Al or an Al alloy, are miniaturized, the level of the electrical resistance becomes significant, which readily causes a wiring delay, lowering the operating speed of the semiconductor device. As a solution, adoption of Cu having a lower electrical resistance value than Al as the wiring material has been considered in recent years. However, Cu becomes oxidized more readily than Al. Accordingly, during the semiconductor manufacturing process, a Cu wiring layer is covered with a layer constituted of a material that does not contain O2, e.g., an SiNx layer, to prevent oxidation of the Cu wiring layer by assuring that it is not exposed to O2.
When connecting a Cu wiring to another wiring in a semiconductor device adopting a multilayer wiring structure, it is necessary to to etch the SiNx layer and to form at the SiNx layer a connecting hole such as a via hole through which the Cu wiring layer is exposed. However, a CF (fluorocarbon) processing gas containing O2 is usually utilized in the plasma etching process during which the SiNx layer is etched. As a result, the surface of the exposed Cu wiring layer becomes oxidized by O2 or an oxide compound is formed at the Cu wiring layer during the etching process. Such a reaction product raises the electrical resistance value at the area where the Cu wiring is connected with the other wiring, thereby presenting a problem in that the device characteristics of the semiconductor device are compromised.
An object of the present invention, which has been completed by addressing the problem of the prior art discussed above, is to provide a new and improved etching method and a new and improved plasma processing method that solve the problem above and other problems.